Fuel cell systems include a fuel cell stack that produces electrical energy based on a reaction between a hydrogen-based feed gas (e.g., pure hydrogen or a hydrogen reformate) and an oxidant feed gas (e.g., pure oxygen or oxygen-containing air). The hydrogen-based feed gas and oxidant feed gas are supplied to the fuel cell stack at appropriate operating conditions (i.e., temperature and pressure) for reacting therein. The proper conditioning of the feed gases is achieved by other components of the fuel cell stack to provide the proper operating conditions.
The fuel cell system includes a compressor for compressing the oxidant feed gas to an appropriate operating pressure for reaction in the fuel cell stack. The compressor also supplies the oxidant feed gas to the fuel cell stack at a flow rate, which is dependent on the electrical load demand from the fuel cell stack. For example, when electrical load demand is increased, the compressor supplies the oxidant feed gas to the fuel cell stack at a higher flow rate.
A mass flow meter is used as a feedback sensor for compressor mass flow control. The flow sensor monitors the mass flow rate of oxidant feed gas through a pipe to the fuel cell stack. Typical mass flow meters are of a hot-wire type that are effected by the flow therethrough. Laminar flow through the pipe results in a steady, accurate signal from the mass flow meter. Turbulent flow, however, results in highly-varying, inaccurate signals. As a result, up to ten pipe diameters of straight pipe length is required before and after the mass flow meter to ensure laminar flow through the mass flow meter. In most applications, however, there is insufficient space to include such long sections of pipe.
One conventional solution includes processing the flow sensor signal through a low pass filter. In this manner, the mass flow meter signal is smoothed, eliminating some of the erroneous data. This, however, still results in an inaccurate mass flow meter signal. Another conventional solution includes incorporating flow straighteners, such as honeycomb flow straighteners, within the pipe. As a result the component count is increased making the overall system more complex and expensive.